1. Field of the Invention
The present invention relates to a fluid bearing apparatus and, more particularly, to a fluid bearing apparatus wherein a thrust bearing includes a dynamic pressure generating groove for generating fluid pressure for supporting the thrust load of a rotating member and a counterflow protecting dynamic pressure generating groove for preventing an operational fluid fed into the dynamic pressure generating groove from counterflowing. This results in an strengthened supporting force of a fluid bearing apparatus, for supporting the rotating member.
2. Description of the Related Art
With the recent improvement of technologies in information media industries such as computers, audio systems, image instruments, and the like, there has been a trend to minimize the sizes of the above media. Accordingly, much smaller, more minute and highly functional devices are required for them.
In the computer industry, a spindle motor of a hard disk driver (HDD) that is one of the memory devices, a scanning motor of a laser printer that is an information instrument, a disk driving motor for reading audio and video signals of a laser disk and a compact disk of an audio system, and in the image displaying industry, a video tape recorder (VTR) head and a camcorder driving apparatus and the like, commonly save, search and read predetermined data by high-speed revolutions of shafts connected to a driving apparatus.
For enhancing the efficiency of the above instruments, super high-speed revolutions of the shafts are required. However, the super high-speed revolutions of the shafts may cause irregular vibrations and oscillations.
The irregular vibrations and oscillations occurring when the shafts are rotated at a super high velocity, may serve as a critical factor of degradation in efficiency of such an accurately operating instrument. Accordingly, each of the instruments includes a bearing that is one of the elements for overcoming the disadvantages associated with the vibrations and oscillations due to the high-speed revolutions of the shafts. Variously modified bearings have recently been provided for solving problems of the shafts by minimizing friction occurring thereon. Among the bearings, fluid bearings using air or oil as an operational fluid are widely used, and are especially suitable for super high-speed revolutions.
FIG. 1 is a cross sectional view of a VTR head driving apparatus and which illustrates the location of a conventional fluid bearing apparatus such as thrust bearing 50, or the thrust bearing 200 of the present invention. The VTR head driving apparatus comprises: an upper drum 20 which is rotatable and on which a head tip 10 is installed, the head tip 10 for reading video and audio signals written on a VTR tape; a fixed lower drum 30 which has the same center as the rotation center of the upper drum 20 and is in contact with the VTR tape at an outer circumference thereof; a thrust bearing 50 having a ring shape, which supports a thrust load of the upper drum 20 and is press-fitted onto a fixed shaft 40; and a rotational power generating unit 60 and 70 for generating power for rotating the upper drum 20 including the head tip 10 at a super high velocity. The reference number 45 represents a hub for connecting a stator 60 of the rotational power generating unit 60 and 70 thereto.
FIG. 2A is a top view of the conventional thrust bearing.
The thrust bearing 50 has a ring shape including a through hole to which the shaft 40 is press-fitted.
The thrust bearing 50 includes a dynamic pressure generating groove 50b on a top surface thereof that contacts with the upper drum 20. The dynamic pressure generating groove 50b generates a predetermined fluid pressure by gathering a fluid in a direction as a result of high-speed rotation of the upper drum 20.
Preferably, the dynamic pressure generating groove 50b has a curved portion 50a that is arranged on a circle (shown by a one-dot chain line in FIG. 2A) established along centers between the inner periphery and the outer periphery of the thrust bearing 50. The curved portion 50a has an inner angle of less than 180 degrees.
The ends of the dynamic pressure generating groove 50b extend to the inner periphery and the outer periphery of the thrust bearing 50, respectively. A plurality of dynamic pressure generating grooves 50b as aforementioned are radially formed around the center of the thrust bearing 50.
The operation of the VTR driving apparatus including the dynamic pressure generating grooves 50b will be described hereinafter.
The upper drum 20 that has been stationary is rotated at a high velocity by the rotational power generating unit 60 and 70. As a result, an operational fluid, such as an oil having a high viscosity, between the top surface of the thrust bearing 50 and the upper drum 20 begins to be rotated in a direction of the rotation of the upper drum 20 due to a boundary friction occurring between solid and fluid.
At this time, the rotated operational fluid is fed into the dynamic pressure generating grooves 50b formed on the top surface of the thrust bearing 50 at a predetermined velocity. After being fed into the dynamic pressure generating grooves 50b, the operational fluid is guided toward the curved portions 50a from the two ends of the dynamic pressure generating grooves 50b, in other words, from the outer periphery of the thrust bearing 50 to the curved portions 50a and from the inner periphery of the thrust bearing 50 to the curved portions 50a. The operational fluid flowing toward the curved portions 50a is then dashed against each other at the curved portions 50a. As a result, the fluid pressure at the curved portions 50a is rapidly increased by a vector sum of the operation fluid flowing in the counter directions against each other (see FIG. 2B).
The fluid pressure is proportional to the number and the area of the dynamic pressure generating grooves 50b, and the rotational velocity of the upper drum 20.
Accordingly, when the fluid pressure generated in the dynamic pressure generating grooves 50b by the rotation of the upper drum 20 becomes larger than the load of the upper drum 20 by rotation of the upper drum 20 by a predetermined velocity, the upper drum 20 is accurately rotated at a constant velocity in spaced apart relation from the thrust bearing 50 by several .mu.m with the operational fluid between the upper drum 20 and the thrust bearing 50.
However, when the operational fluid is rotated by the boundary friction, the rotated fluid changes its movement in the opposite direction, i.e., from the center of the thrust bearing to the outer periphery of the thrust bearing due to the inertia force and the centrifugal force thereof. As a result, in the dynamic pressure generating grooves, the operational fluid does not flow toward the curved portions. Conversely, the operational fluid counterflows in the opposite direction, i.e., from the curved portions to the inner periphery of the thrust bearing and the outer periphery of the thrust bearing.